1. Field of the Invention
The present invention relates to an optical transmission system using an optical fiber as an optical transmission path and a dispersion-compensating optical fiber for the optical transmission system.
2. Description of the Related Art
A holey fiber is a new type of optical fiber including a core region formed at a center of the optical fiber and a cladding region having a plurality of holes that are arranged around the core region at regular intervals, where the holes reduce the average refractive index of the cladding region. The light is transmitted in the core region by the principle of the total reflection of light. The holey fiber can achieve special characteristics such as an endlessly single mode (ESM), which cannot be achieved by a conventional optical fiber, by controlling the refractive index using the holes. In the ESM, there is no cutoff wavelength and a light having any wavelength can be transmitted in single mode. In other words, in the holey fiber, a light signal having a wavelength in any one of the band from 1260 nm to 1360 nm and the E band from 1360 nm to 1460 nm, as well as the S band from 1460 nm to 1530 nm, the C band from 1530 nm to 1565 nm, and the L band from 1565 nm to 1610 nm can be transmitted in single mode, enabling a high-speed optical transmission over a broad bandwidth.
Results of broadband optical transmission tests using broadband characteristics of the holey fiber have been reported (see, for example, K. Nakajima, et al., “Ultra wide band 190 Gbit/s WDM transmission over a long length and low loss PCF”, Proc. OFC PDP23 (2004) and K. Ieda, et al., “Visible to Infrared WDM transmission over PCF”, ECOC2006-Tu3.3.4 (2006)). In addition, a result of a test of dispersed-managed Soliton transmission at a transmission rate of 10 Gb/s, in which an optical transmission path of 100 km including a holey fiber and a dispersion-compensating optical fiber is used, has been reported (see, for example, K. Kurokawa, et al., “Penalty-Free Dispersion-Managed Soliton Transmission over 100 km Low Loss PCF”, Proc. OFC PDP21 (2005)).
However, according to the first two literatures, optical transmission is performed without compensating a large wavelength dispersion of the holey fiber. Therefore, high transmission rate cannot be achieved and a transmission distance is short. On the other hand, according to the third literature, the wavelength dispersion of the holey fiber is compensated using a dispersion-compensating optical fiber. However, only the C band is used as an operation wavelength band for optical transmission and the broadband characteristics of the holey fiber are not utilized.